It’s /mnt/JAILDRIVENAME/iocage/jails/PLEXJAILNAME/root/usr/local/plexdata-plexpass
( if you’re doing this from within the jail it’s just /usr/local/plexdata-plexpass )
If you didn’t move it somewhere else it’s using this default location. You might try applying a chown -R plex:plex to this, in case the files are not all owned by Plex so it cannot modify them right now.
But I wouldn’t worry about that until you can reach the server from the local IP at least.
